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Onagawa Nuclear Power Plant

Coordinates: 38°24′04″N 141°29′59″E / 38.40111°N 141.49972°E / 38.40111; 141.49972
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Onagawa Nuclear Power Plant
The Onagawa Nuclear Power Plant
Coordinates38°24′04″N 141°29′59″E / 38.40111°N 141.49972°E / 38.40111; 141.49972
StatusOut of service for 13 years, 4 months
Construction beganJuly 8, 1980 (1980-07-08)
Commission dateJune 1, 1984 (1984-06-01)
Operator(s)Tohoku Electric Power Company
Nuclear power station
Reactor typeBWR
Power generation
Units operational1 x 524 MW
2 x 825 MW
Nameplate capacity2,174 MW
Capacity factor0%
Annual net output0 GW·h
External links
Websitewww.tohoku-epco.co.jp/genshi/onagawa/index.html, English version
CommonsRelated media on Commons

The Onagawa Nuclear Power Plant (女川原子力発電所, Onagawa (pronunciation) genshiryoku hatsudensho, Onagawa NPP) is a nuclear power plant located on a 1,730,000 m2 (432 acres) site[1] in Onagawa in the Oshika District and Ishinomaki city, Miyagi Prefecture, Japan. It is managed by the Tohoku Electric Power Company. It was the most quickly constructed nuclear power plant in the world.[citation needed]

All the reactors were constructed by Toshiba.[2] The Onagawa-3 unit was used as a prototype for the Higashidori Nuclear Power Plant.[3]

The plant was shut down after the 2011 Tōhoku earthquake and tsunami. The Onagawa nuclear power plant was the closest nuclear power plant to the epicenter, and facing the Pacific Ocean on Japan's north-east coast, experienced very high levels of ground shaking – among the strongest of any plant affected by the earthquake – and some flooding from the tsunami that followed.[4] All three reactors at the power plant successfully withstood the earthquake and tsunami without accident.[5]

Following an IAEA inspection in 2012, the agency stated that "The structural elements of the NPS (nuclear power station) were remarkably undamaged given the magnitude of ground motion experienced and the duration and size of this great earthquake".[4][6] More recently, Tohoku Electric reported that the third floor of No. 2 reactor building lost about 70% of its structural rigidity and the first floors lost 25%, compared to when they were built, and was planning to reinforce the structures for increased quake resistance.[7] In 2013 the station operators sent an application request to restart unit 2 at Onagawa to the Japanese Nuclear Regulation Authority (NRA).[8] Reactor 2 was expected to be restarted in 2021 following upgrade work,[9] but the starting date has since been postponed to September 2024.[10]


Unit Type[11] Start construction First criticality Commercial operation Electric Power Comments
Onagawa – 1 BWR 8 July 1980 18 October 1983 1 June 1984 524 MW To be decommissioned
Onagawa – 2 BWR 12 April 1991 2 November 1994 28 July 1995 825 MW Start-up pending
Onagawa – 3 BWR 23 January 1998 26 April 2001 30 January 2002 825 MW Start-up pending

It was announced in 2018, that Onagawa Unit 1 which has been idled since 2011 will be decommissioned. Tohoku Electric also plans to resume operations of the Onagawa Unit 2 reactor in 2020-21 following significant safety improvements.[12]

Environmental impact


The plant conforms fully to ISO 14001, a set of international environmental management standards. The plant's waste heat water leaves 7 degrees Celsius higher than it came in and is released 10 meters under the surface of the water, in order to reduce adverse effects on the environment.[13]



2005 Miyagi earthquake


The Onagawa Nuclear Power Plant was affected by the 2005 Miyagi earthquake and recorded vibrations above what the plant was designed for. Analysis after the event, however, found no damage to the reactor systems. Some people reported seeing smoke come from the plant after the earthquake and reported it, thinking that it indicated an accident, but the smoke was actually produced by the backup diesel generators.[citation needed]

2011 Tōhoku earthquake

The estimated tsunami heights before making landfall, from destroyed buoy gauges. Alternatively, from a 25 March 2011 report made by the Port and Airport Research Institute (PARI), which determined tsunami height by visiting the port areas, the Fishery port of Onagawa experienced 15 m (50 ft), the highest of all surveyed areas.[14]

The Onagawa Nuclear Power Plant was the closest nuclear power plant to the epicenter of the 2011 Tōhoku earthquake,[15] less than half the distance of the stricken Fukushima I power plant.[16] The town of Onagawa to the northeast of the plant was largely destroyed by the tsunami[17] which followed the earthquake, but the plant's 14 meters (46 ft) high seawall was tall and robust enough to prevent the power plant from experiencing severe flooding. Yanosuke Hirai, who died in 1986, is cited as the only person on the entire power station construction project to push for the 14.8-meter breakwater. Although many of his colleagues regarded 12 meters as sufficient, Hirai's authority eventually prevailed, and Tōhoku Electric spent the extra money to build the 14.8m tsunami wall. Another of Hirai's proposals also helped ensure the safety of the plant during the tsunami: expecting the sea to draw back before a tsunami, he made sure the plant's water intake cooling system pipes were designed so it could still draw water for cooling the reactors.[18][better source needed]

All safety systems functioned as designed, the reactors automatically shut down without damage, and no reactor damage occurred.[19] A fire broke out in the turbine hall,[20][21][22] which is sited separately from the plant's reactor[23] in a building housing the electricity-generating turbine, but was soon extinguished.[24]

Following the tsunami, two to three hundred residents of the town who lost their homes to the tsunami took refuge in the Onagawa nuclear plant's gymnasium, as the reactor complex was the only safe area in the vicinity to evacuate to, with the reactor operators supplying food and blankets to the needy.[25] At the time Reuters suggested that the Onagawa nuclear power plant may demonstrate that it is possible for nuclear facilities to withstand the greatest natural disasters, and to retain public trust.[5] The plant was shut down following the earthquake and tsunami, in accordance with standard legally mandated procedure after such an event,[26] but despite the IAEA finding that the plant had survived the quake remarkably undamaged,[27] the three units remain in cold shutdown. Whereas the mishaps at Fukushima I radically changed public opinion on safety and risks, Tohoku Electric seems to have preserved much of its pre-disaster goodwill in the area of Onagawa.[5] While the tsunami was more than 13m high at both Fukushima I and the Onagawa power plant,[18] the largest difference between them, apart from the reactor safety systems being designed some twenty years apart, was that the Fukushima I seawall was built to a height of just 5.7m, while the Onagawa power plant seawall was nearly 14 m (46 ft) high and thus successfully blocked the majority of the tsunami from causing severe flood damage.[18] It was this tsunami that has been determined to be solely responsible for precipitating the loss of cooling and ultimately the Fukushima disaster at Fukushima I which had a much shorter sea wall of 5.7 m (19 ft).[28] In response to the high tsunami, Onagawa power plant's seawall was later built up to a height of 17 m (56 ft).[29]

On 13 March 2011, two days after the earthquake and tsunami, levels of radiation on site reached 21μSv/hour, a level at which Tohoku Electric Power Company were mandated to declare a state of emergency, and they did so at 12:50, declaring the lowest-level such state. Within 10 minutes the level had dropped to 10μSv/hour.[30][31][32] The Japanese authorities believe the temporarily heightened values were due to radiation from the Fukushima I nuclear accidents and not from the Onagawa plant.[33][34] On 13 March, 20:45 UTC, the IAEA announced that radiation levels at the Onagawa plant had returned to normal background levels.[33]

An 7 April 2011 aftershock damaged 2 of the 3 power lines connecting to the plant, but it did not damage any of the backup cooling systems, which remained undamaged and unneeded, including the ESWS, the ECCS and the back up diesel generators.[35]

2013-2019 reactor restart requests


In 2013 the owners of the station, Tohoku Electric Power Company, sent a restart request to the Nuclear Regulation Authority (NRA) for Onagawa 2.[8] They can only be restarted after passing an assessment by the Nuclear Regulatory Agency, which in turn is waiting on completion of construction of newly-required safety measures. The utility company expected to complete construction by March 2019, and planned to restart Onagawa 2 by fiscal year 2020.[36]

In November 2019 the NRA gave approval for Onagawa 2 to be restarted subject to local approvals, consultation and further anti-disaster work.[37][38][9] The reactor was expected to be restarted in 2021 following upgrade work.

In contrast, Onagawa 1 has been slated for decommissioning, the tenth operable reactor to do so since the Fukushima Daiichi nuclear disaster.[36] Costs of bringing Onagawa 1 to the standards set by the Nuclear Regulation Authority and subsequent maintenance are considered too expensive and time-consuming in comparison to the other two units. Further complicating the issue, a new rule was set by the NRA in the wake of the Fukushima disaster which limits the operational life of nuclear reactors to 40 years. Onagawa 1 has operated since 1984, and therefore would only be able to operate a few more years even if it were approved to restart.[39]

See also



  1. ^ Tohoku Power. The Onagawa Plant (information) Archived 21 March 2011 at the Wayback Machine.
  2. ^ Toshiba. Nuclear List of Delivered Units Archived 2 September 2011 at the Wayback Machine.
  3. ^ Tohoku Power. Higashidori Nuclear Power Station.
  4. ^ a b Section, United Nations News Service (10 August 2012). "UN News – Japanese nuclear plant 'remarkably undamaged' in earthquake – UN atomic agency". Retrieved 7 February 2017.
  5. ^ a b c "Japanese nuclear plant survived tsunami, offers clues". Reuters. 20 October 2011.
  6. ^ "IAEA Expert Team Concludes Mission to Onagawa NPP". 10 August 2012. Retrieved 7 February 2017.
  7. ^ "1,130 cracks, 70% rigidity lost at Onagawa reactor building:The Asahi Shimbun". Archived from the original on 19 January 2017. Retrieved 20 December 2020.
  8. ^ a b "Tohoku seeks Onagawa 2 restart". Retrieved 7 February 2017.
  9. ^ a b "Regulator confirms Onagawa 2 meets Japanese nuclear safety requirements". Retrieved 14 September 2020.
  10. ^ "Onagawa 2 restart expected in September". World Nuclear News. 20 February 2024. Retrieved 15 April 2024.
  11. ^ "Reactors in operation". IAEA. 31 December 2009. Retrieved 15 March 2016.
  12. ^ "Tohoku Electric to scrap aging No. 1 unit at Onagawa nuclear plant". Japan Times. 25 October 2018. Retrieved 12 October 2019.
  13. ^ Tohoku Power. Onagawa Nuclear Power Station.
  14. ^ 行政情報システム室 (25 March 2011). "Executive Summary of Urgent Field Survey of Earthquake and Tsunami Disasters by the 2011 off the Pacific coast of Tohoku Earthquake" (PDF). Yokosuka, Japan: Port and Airport Research Institute (PARI). Archived from the original (PDF) on 13 June 2013. Retrieved 12 March 2012.
  15. ^ "Plant weathered Japan quake well: IAEA – Taipei Times". Retrieved 7 February 2017.
  16. ^ http://nsspi.tamu.edu/pauloscornerarticles/2012-08/iaea-japan-nuclear-plant-closer-than-fukushima-to-quake-epicenter-is-remarkably-undamaged [dead link]
  17. ^ Higgins, Andrew (17 March 2011). "In Onagawa, Japan's tsunami destroys community". The Washington Post.
  18. ^ a b c Venkataraman, Bina (6 February 2019). "The Optimist's Telescope: Thinking Ahead in a Reckless Age". The Economist.
  19. ^ Yamaguchi, Mari, Associated Press, "Nuke plant near quake epicenter undamaged", Stars and Stripes, 11 August 2012, p. 8
  20. ^ Mogi, Chikako (11 March 2011). "Fire at Tohoku Elec Onagawa nuclear plant". Reuters. Kyodo | Reuters. Retrieved 13 March 2011.
  21. ^ "Japan initiates emergency protocol after earthquake – Nuclear Engineering International". Retrieved 7 February 2017.
  22. ^ Mogi, Chikako (11 March 2011). "Fire at Tohoku Elec Onagawa nuclear plant -Kyodo | Reuters". Reuters. Archived from the original on 21 April 2011. Retrieved 13 March 2011.
  23. ^ McCurry, Justin (11 March 2011). "Japan's Fukushima nuclear plant under state of emergency after quake". The Guardian. London.
  24. ^ "Fire at nuclear power plant extinguished". The Australian. 12 March 2011. Archived from the original on 21 April 2011. Retrieved 13 March 2011.
  25. ^ Ito, Shingo (Agence France-Presse/Jiji Press), "Neighbors of Miyagi reactor mull getting out", Japan Times, 1 April 2011, p. 3.
  26. ^ Hafez Ahmed @ http://www.thefinancialexpress-bd.com. "March 2011 Japan's atomic plant neighbours mull leaving homes". Thefinancialexpress-bd.com. Archived from the original on 28 July 2011. Retrieved 7 September 2011. {{cite web}}: External link in |author= (help)
  27. ^ "Onagawa plant 'remarkably undamaged,' says IAEA". Retrieved 7 February 2017.
  28. ^ "Earthquake not a factor in Fukushima accident". Retrieved 7 February 2017.
  29. ^ Yamaguchi, Mari (10 August 2012). "IAEA: Nuke plant near Fukushima largely undamaged". Boston.com. Retrieved 7 February 2017.
  30. ^ "Contamination checks on evacuated residents". world-nuclear-news.org. 2011. Retrieved 13 March 2011. A technical emergency was declared at 12.50 pm today at the Onagawa nuclear power plant after radiation levels in the plant site reached 21 microSieverts per hour. At this level plant, owner Tohoku Electric Power Company is legally obligated to inform government of the fact. Within just ten minutes, however, the level had dropped to 10 microSieverts per hour.
  31. ^ "IAEA update on Japan Earthquake". iaea.org. 13 March 2011. Retrieved 13 March 2011. Japanese authorities have also informed the IAEA that the first (i.e., lowest) state of emergency at the Onagawa nuclear power plant has been reported by Tohoku Electric Power Company. The authorities have informed the IAEA that the three reactor units at the Onagawa nuclear power plant are under control. As defined in Article 10 of Japan's Act on Special Measures Concerning Nuclear Emergency Preparedness, the alert was declared as a consequence of radioactivity readings exceeding allowed levels in the area surrounding the plant. Japanese authorities are investigating the source of radiation.
  32. ^ Chico Harlan, Steven Mufson: Japanese nuclear plants' operator scrambles to avert meltdowns. The Washington Post, 11 March 2011
  33. ^ a b IAEA (2011). "Fukushima Nuclear Accident Update Log – Updates of 13 March 2011". iaea.org. Retrieved 13 March 2011.
  34. ^ "Sea water injected into troubled Fukushima power plant | The Manila Bulletin Newspaper Online". mb.com.ph. 2011. Retrieved 13 March 2011. Meanwhile, radiation monitored at the Onagawa nuclear power plant in Miyagi Prefecture on the Pacific coast shot up on Sunday, Tohoku Electric Power Co. said, adding that it was likely caused by radioactive substances let out at the troubled Fukushima No. 1 nuclear power plant in Fukushima Prefecture.
  35. ^ Japan earthquake today: Tsunami warning lifted, but Fukushima evacuated, Christian Science Monitor, Gavin Blair, 7 April 2011
  36. ^ a b "Tohoku decides to decommission oldest Onagawa unit – World Nuclear News". www.world-nuclear-news.org. Retrieved 27 November 2018.
  37. ^ "Japan clears restart at nuclear reactor closest to epicenter of 2011 quake". Reuters. Retrieved 14 September 2020.
  38. ^ "Tohoku reactor restart: What is the state of Japan's nuclear policy?". Retrieved 14 September 2020.
  39. ^ "Tohoku Electric to scrap aging Onagawa nuke plant reactor over maintenance costs". Mainichi Daily News. 26 October 2018. Retrieved 27 November 2018.